The specific aim of this project is to search for measurable, reliable electrophysiologic changes in human subjects that correspond to the presence or absence of masking level differences in the same subjects. Normal listeners serve as control subjects, and persons with VIIIth nerve/brainstem disorders serve as experimental subjects. Following audiologic, and for the experimental subjects, otologic and neurologic evaluations, late cortical and select brainstem potential patterns are studied under two tone/noise phase conditions: SoNo and SPiNo. The resulting potentials are computer stored and later analyzed for differences in latency and amplitude. Behavioral masking level differences are also measured for these subjects. The long-term goal of the project is the definition of the electrical profile of both homophasic and antiphasic listening conditions, e.e., and "objective" measure of binaural masking level differences and thus of the integrity of binaural auditory processes in the human auditory brainstem. A related benefit will be data which should provide indirect evidence of the site(s) from which masking level differences arise.